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Your experience with Air/Oil separator

Your experience with Air/Oil separator

  • I installed one and finds it very effective with no oil on the belly

    Votes: 20 22.7%
  • I installed one which drastically reduced oil on belly

    Votes: 39 44.3%
  • I did not install one and run the engine with lower oil level

    Votes: 19 21.6%
  • I am planning on installing one

    Votes: 12 13.6%

  • Total voters
    88
  • Poll closed .

Bavafa

Well Known Member
Just curious how many people have installed an air/oil separator and how much did it improve. It will probably be helpful if one brand has proven to be more effective than the other.

I accidentally posted this in the classified section. Would appreciate help in moving it to general section.
 
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I installed the ACS unit and it was a poor performer. Installed the antisplat version and it works well to control oil on the belly. Doesn't eliminate it, but significantly reduces it.

Larry
 
I installed the ACS unit and it was a poor performer. Installed the antisplat version and it works well to control oil on the belly. Doesn't eliminate it, but significantly reduces it.

Larry

Same experience here with the Anti-Splat. You will need to clean out the exhaust check valve at least annually, but it is quite effective in limiting oil on the belly.
 
I have the antisplat 540 version on my 360, i do not have the version that ties into the exhaust. I maintain the oil level at about 7qts. I have seen no sign of any oil out of the breathet. I do get a tiny bit of oil on the belly from s slow leak i still need to find.
 
Survey needs another option- I choose to NOT use a separator because X Quarts
(6 for my 0-320) is a good level and my breather is properly located.

I put the breather in a happy spot with a 45 degree bias cut outlet. 6 qts, no residue.

Used to have it blow vertically with a 1 inch gap on the left side crossover exhaust, above the bottom of the firewall. That was a mistake. Had all sorts of little leaks that are now gone. That was too high a pressure area. 4 quarts was the least I tried and all results were the same. Not too big a loss of oil, but seeps galore from too much crankcase pressure.

I guess I could try 7 and 8 quarts and see wherethe throwaway point is.

It now exits at the aft end of the coal shovel stock outlet where it should not freeze but has a bit of vacuum.
 
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I can't resist throwing out this video and associated analogy (read the YouTube comment :p) from Mike Busch -

https://www.youtube.com/watch?v=2_pRXfPp5wQ

Except it's not the whole story.

Mike's cup 'o **** is exactly what is to be expected if the separator's liquid output is routed to a catch bottle. Each cold start feeds condensed water to the bottle, as the breather gas and separator are not yet hot enough to keep the water in vapor phase. Later, if kept hot, all that water goes overboard.

https://www.danhorton.net/Articles/Separator-or-Condenser.pdf
 
Catch container?

Is there a reason not to just have a well vented catch container on the lower part of the firewall with the overflow tube going directly into it? (I do understand inverted flight would be an issue...)
 
Great article Dan !

Not thrilled with Mike Busch's effort though, especially when you relate it to a lot of RV's.

If you are in a cruiser, don't aerobat, keep your oil level at a sensible level - probably at least a quart below full, and change your oil regularly - 25 hrs/4 months, then you should have a healthy engine for life and don't need a separator.

However, if you like the sporting life and don't have a Raven or Christen system, these separator/catchers are invaluable to keep from having a wet belly and yes, we drain the oil straight back into the sump, where it belongs !

We have the Andair system and include a condensate trap. The separator does an excellent job of catching gobs when we draw a line or do a really good hammerhead... The condensate catcher does a fine job of catching milky goo when stood, at start etc etc and gets cleaned regularly.

Cruiser - probably no need :)

Mild stunter - definitely :D

Big stunter - man up and get an inverted system ;)
 
Is there a reason not to just have a well vented catch container on the lower part of the firewall with the overflow tube going directly into it? (I do understand inverted flight would be an issue...)

If by "overflow tube" you mean the line which drains separated liquid from the separator can, a catch bottle will work. See Fig.1 in the linked article.

However, it's awkward. Gotta pull the cowl to dump it, gotta have a place to dump it, it can still wet the engine compartment, etc.
 
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Sorry, poor choice of terminology on my part. I meant the actual engine breather hose going into a catch bottle, with no separator installed at all.

Your comments would still be appropriate. Aside from those, just wondering if there's any problem using a catch bottle that might affect engine operation?

Thanks,
Tom

If by "overflow tube" you mean the line which drains separated liquid from the separator can, a catch bottle will work. However, it's awkward. Gotta pull the cowl to dump it, gotta have a place to dump it, it can still wet the engine compartment, etc.
 
Sorry, poor choice of terminology on my part. I meant the actual engine breather hose going into a catch bottle, with no separator installed at all.

Your comments would still be appropriate. Aside from those, just wondering if there's any problem using a catch bottle that might affect engine operation?

Thanks,
Tom

It will make a mess. The breather hose coughs out aerosol oil droplets. They will probably remain aerosol and simply exit the bottle vent, rather than collecting in the bottle.
 
It will make a mess. The breather hose coughs out aerosol oil droplets. They will probably remain aerosol and simply exit the bottle vent, rather than collecting in the bottle.

yes, I just went through the experiment of a catch can without a closed top. It was a water bottle with the crank case breather hose dropped down into it.

The oil from the breather tube misted my firewall and everything else just aft of the engine. If you could install something like a sponge on top of the catch can so as not to be air tight, but stop the misted oil from escaping, it seems that would work.
 
A real air-oil separator functions on two primary variables. Surface area (larger better) within, and velocity (slower better). The Anti-splat has its partial success with a clever internal centrifugal action for larger particles. If they are small, like aerosols, they either come in contact with something and stick or follow the airstream.

Note the airwolf units have lots of surface area and volume to slow the flow. They work pretty well.

Now to the capture and return. Why worry? That is just a small sample of what is in the bottom of the crankcase anyway after the shutdown blow-by (with it's 145F dew point) condenses. Trying to address the stuff in the blow-by can does not really solve a problem.
 
I used to lose huge amounts of oil and have a dripping wet belly after every aerobatic flight. The Raven "half" system (essentially a glorified air-oil separator) worked great to solve this problem. I just ordered parts to make it a full inverted system (to allow oil pressure under sustained inverted/ negative G flight). If you don't fly aerobatics, you may not need an air-oil separator if you don't fill above 6qts.
 
Thank you all for providing your experience and feedback.

For those with a IO390 engine, where did you plumb your return oil line back to the engine? On a O360 engine, there is a hex plug next to the governor pad but not sure if this plug exist in a 390 engine.
 
Air Oil Separator

Same experience here with the Anti-Splat. You will need to clean out the exhaust check valve at least annually, but it is quite effective in limiting oil on the belly.

We installed the Anti Splat Air/Oil Separator with exhaust check/vacuum valve that develops a very slight negative pressure on the engine crankcase. Huge improvement on oil residue on the belly. It also increased RPM at takeoff. Easier explanation of all that on Anti-Splats website.
***CAUTION*** YOU MUST INSPECT THE CHECK VALVE AND CLEAN ANY CARBON RESIDUE OUT OF THE VACUUM VALVE EVERY 100 HOURS OR ANNUALLY.
 
We installed the Anti Splat Air/Oil Separator with exhaust check/vacuum valve that develops a very slight negative pressure on the engine crankcase. Huge improvement on oil residue on the belly. It also increased RPM at takeoff.

How much increase? Theory says it should.

***CAUTION*** YOU MUST INSPECT THE CHECK VALVE AND CLEAN ANY CARBON RESIDUE OUT OF THE VACUUM VALVE EVERY 100 HOURS OR ANNUALLY.

Thanks for mentioning that Milon. It cannot be stressed enough.

Rather than "100 hours or annually", I'd suggest developing a cleaning schedule based on early observation of the particular installation. Technically, it is not the valve which needs cleaned, but rather, the tubular tap into the exhaust system. There have been reports of total blockage at less than 50 hours for Anti-Splat RV-10 exhaust taps mounted on the tailpipe. Even after establishing a rate of accumulation, I'd keep an eye on it, as it may accumulate coke more rapidly as the engine ages and puts more oil out the breather. A change in the usual operating RPM can also make a difference.

Exhaust tap on my 390. It's welded, not clamped. Note bracing; I'm not a big fan of just welding a tube into a hot, vibrating header pipe and allowing it to cantilever without support. The disk is a heat sink; the reed valve stays cool (yes, I measured).

Tap.jpg


This is the coking problem. The little bit of aerosol oil which reaches the hot exhaust tap can accumulate and eventually block the tap. It seems to build up as a ring of material, but individual applications may vary.

Coked%20Oil.jpg


The tap as shown would go more than 140 hours without blockage. One experiment was to see if the rate of accumulation could be slowed even more by installing an insulated liner tube:

Tube%20Insertion.jpg


It's been in there a few hundred hours now. I clean with an appropriately sized drill bit at each 50 hour oil change, so I've had plenty of opportunity for observation. In my opinion, it didn't result in any significant improvement. Although it may accumulate coke at a slower rate, the smaller ID is faster to block. I'll probably remove the liner tube the next time the pipes are off the engine.

In any case, all installations should have a relief valve tee'd into the line between the separator and the exhaust tap. It's the same NAPA #2-29000 reed valve, installed so vacuum keeps it shut and positive pressure cause it to open. It just sits there doing nothing most of the time, but if the exhaust tap should coke shut, engine case pressure will vent via the relief valve and the engine won't blow seals. I'm aware of at least one instance where it happened and the relief worked, so just do it.

This particular relief valve has had the integral mounting nut machined off to save a few ounces.

Shortened%20Relief%20Valve%20Tube.jpg
 
I made a simple one out of aluminum tubing and some aluminum bar stock. It is mounted such that it simply drains back into the breather port on the back of the engine but is otherwise derived from Tony Bingelis' design. Dropping the velocity and providing lots of surface area for the droplets to coalesce onto are key.

24180650251_205de941bd_z.jpg


Filling with eight quarts of oil after an oil change then flying for an hour leaves the belly clean and dry. Can't ask much more of it.
 
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No air/oil separator here; none needed. I clean the belly once a year at annual, and there's not that much accumulation.

Lighter, simpler, less expensive.
 
There have been reports of total blockage at less than 50 hours for Anti-Splat RV-10

How much increase? Theory says it should.



Thanks for mentioning that Milon. It cannot be stressed enough.

Rather than "100 hours or annually", I'd suggest developing a cleaning schedule based on early observation of the particular installation. Technically, it is not the valve which needs cleaned, but rather, the tubular tap into the exhaust system. There have been reports of total blockage at less than 50 hours for Anti-Splat RV-10 exhaust taps mounted on the tailpipe. Even after establishing a rate of accumulation, I'd keep an eye on it, as it may accumulate coke more rapidly as the engine ages and puts more oil out the breather. A change in the usual operating RPM can also make a difference.

Exhaust tap on my 390. It's welded, not clamped. Note bracing; I'm not a big fan of just welding a tube into a hot, vibrating header pipe and allowing it to cantilever without support. The disk is a heat sink; the reed valve stays cool (yes, I measured).

Tap.jpg


This is the coking problem. The little bit of aerosol oil which reaches the hot exhaust tap can accumulate and eventually block the tap. It seems to build up as a ring of material, but individual applications may vary.

Coked%20Oil.jpg


The tap as shown would go more than 140 hours without blockage. One experiment was to see if the rate of accumulation could be slowed even more by installing an insulated liner tube:

Tube%20Insertion.jpg


It's been in there a few hundred hours now. I clean with an appropriately sized drill bit at each 50 hour oil change, so I've had plenty of opportunity for observation. In my opinion, it didn't result in any significant improvement. Although it may accumulate coke at a slower rate, the smaller ID is faster to block. I'll probably remove the liner tube the next time the pipes are off the engine.

In any case, all installations should have a relief valve tee'd into the line between the separator and the exhaust tap. It's the same NAPA #2-29000 reed valve, installed so vacuum keeps it shut and positive pressure cause it to open. It just sits there doing nothing most of the time, but if the exhaust tap should coke shut, engine case pressure will vent via the relief valve and the engine won't blow seals. I'm aware of at least one instance where it happened and the relief worked, so just do it.

This particular relief valve has had the integral mounting nut machined off to save a few ounces.

Shortened%20Relief%20Valve%20Tube.jpg

I completely agree with Dan?s statement about cleaning every 50 hours at oil change. The first 50 hours ours showed some accumulation of gunk. It decreased every 50 hours thereafter. We gained about 75 RPM.
 
There have been reports of total blockage at less than 50 hours for Anti-Splat RV-10

How much increase? Theory says it should.



Thanks for mentioning that Milon. It cannot be stressed enough.

Rather than "100 hours or annually", I'd suggest developing a cleaning schedule based on early observation of the particular installation. Technically, it is not the valve which needs cleaned, but rather, the tubular tap into the exhaust system. There have been reports of total blockage at less than 50 hours for Anti-Splat RV-10 exhaust taps mounted on the tailpipe. Even after establishing a rate of accumulation, I'd keep an eye on it, as it may accumulate coke more rapidly as the engine ages and puts more oil out the breather. A change in the usual operating RPM can also make a difference.

Exhaust tap on my 390. It's welded, not clamped. Note bracing; I'm not a big fan of just welding a tube into a hot, vibrating header pipe and allowing it to cantilever without support. The disk is a heat sink; the reed valve stays cool (yes, I measured).

Tap.jpg


This is the coking problem. The little bit of aerosol oil which reaches the hot exhaust tap can accumulate and eventually block the tap. It seems to build up as a ring of material, but individual applications may vary.

Coked%20Oil.jpg


The tap as shown would go more than 140 hours without blockage. One experiment was to see if the rate of accumulation could be slowed even more by installing an insulated liner tube:

Tube%20Insertion.jpg


It's been in there a few hundred hours now. I clean with an appropriately sized drill bit at each 50 hour oil change, so I've had plenty of opportunity for observation. In my opinion, it didn't result in any significant improvement. Although it may accumulate coke at a slower rate, the smaller ID is faster to block. I'll probably remove the liner tube the next time the pipes are off the engine.

In any case, all installations should have a relief valve tee'd into the line between the separator and the exhaust tap. It's the same NAPA #2-29000 reed valve, installed so vacuum keeps it shut and positive pressure cause it to open. It just sits there doing nothing most of the time, but if the exhaust tap should coke shut, engine case pressure will vent via the relief valve and the engine won't blow seals. I'm aware of at least one instance where it happened and the relief worked, so just do it.

This particular relief valve has had the integral mounting nut machined off to save a few ounces.

Shortened%20Relief%20Valve%20Tube.jpg

I completely agree with Dan?s statement about cleaning every 50 hours at oil change. The first 50 hours ours showed some accumulation of gunk. It decreased every 50 hours thereafter.
 
I installed an AntiSplat oil mist separator with the collected oil drained back to the crankcase. However, we routed the vent line overboard in the vicinity of the exhaust outlet. Did not tie the vent line back into the hot exhaust to avoid potential coking/plugging problems. Works fine and greatly reduced oil on the belly versus w/o the separator.

The main contaminant on my belly is lead deposits from the engine exhausts.
 
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